This library provides Clojure-style multimethods for Emacs Lisp, supporting multiple dispatch over an ad hoc type hierarchy.
See also: Clojure-style Multimethods in Emacs Lisp.
;; `vector' is the dispatch function for the multimethod `show'
(predd-defmulti show #'vector
"Return how an animal should respond when shown another animal.")
(predd-defmethod show [:cat :mouse] (a b)
:chase)
(predd-defmethod show [:cat :dog] (a b)
:run)
(predd-defmethod show [:dog :cat] (a b)
:bark)
;; Call the multimethod on some different types
(show :cat :dog) ; => :run
(show :cat :mouse) ; => :chase
;; Declare that a tabby is a specific type of cat.
(predd-derive :tabby :cat)
(show :dog :tabby) ; => :bark